Ann: Change of Director's Interest Notice, page-4

If you buy too many in one go as I found out, it can make the share price jump for the day.You then have to explain your self.
You may think no big deal if the order is just a few thousand dollars. But its the effect of even that small order. I think its a 20% rise that triggers queries, even if the next day, the price is back to where it was.

Buying in not over the top amounts is how they have to so that they dont get accused of market shenanigans. Several smaller buys rather than bigger chunkier amounts, especially when liquidity is lowish, is the responsible way to increase your position..